Systemic Lupus Erythematosus (SLE) is an autoimmune disease that causes significant morbidity and mortality. Its prevalence is 400 cases per 100,000 in African American women. SLE affects multiple organ systems, but renal manifestations are the primary contributor to the morbidity of this disease, and immunosuppressive agents are required to slow progression to end stage renal disease. SLE is characterized by loss of tolerance to self nucleic acids. The source of autoantigen that drives disease onset and progression is unclear. Apoptotic cells are a suggested source, and genetic defects in clearance of dead cells are associated with lupus-like syndromes. However, no direct evidence of the role of apoptotic cells in vivo has been obtained, nor is it clear what the cellular sources of apoptotic debris are. To understand this would be very important, as it could explain the initiation of lupus, events that trigger exacerbations, and genetic predisposition to disease. A novel candidate source of autoantigen is a unique form of neutrophil cell death in which cells release DNA into the extracellular environment, generating a structure known as a neutrophil extracellular trap, or NET. Though several groups studying NETs have suggested they may provide lupus autoantigens in vivo, paradoxically, it has been observed that humans with an X-linked defect in NADPH oxidase and hence chronic granulomatous disease (CGD), whose neutrophils cannot form NETs have an increased predisposition to SLE. Indeed, even the carrier mothers of CGD patients have an almost 10-fold increased risk of lupus. The goal of my PhD thesis and this proposal is to investigate the role that NETs and NADPH oxidase play in the pathogenesis of SLE. Based on the disease predisposition in humans and our preliminary data, we hypothesize NETs are not an important source of autoantigen in SLE but rather represent a normal way of safely processing self-DNA to prevent it from being autoimmunogenic. Furthermore, we propose that the NADPH oxidase enzyme, which is required for NET formation, inhibits SLE pathology. We will test this hypothesis by using the murine model of CGD, which lacks functional NADPH oxidase and cannot form NETs. In the first Aim, this mutation will be crossed to the MRL/lpr and B6 Fc3RIIb models of SLE to determine the role NETs play in disease pathogenesis. In the second Aim the role of NADPH oxidase in reducing disease pathology will be examined mechanistically using cellular and molecular approaches. This proposal addresses a high-profile question regarding the importance of NETs as autoantigens in SLE. Our mechanistic studies into the role of NADPH oxidase in autoimmunity will not only provide insight into the predisposition to SLE that has been noted in patients with CGD, but will also improve understanding of disease initiation and maintenance. Ultimately this may lead to new therapeutic targets for lupus nephritis.